Apparatus for applying an end plug to an end of a fuel rod tube

ABSTRACT

An improved apparatus for applying an end plug to an end of a fuel rod tube includes a housing having spaced inlet and outlet ends adapted to receive the end plug and tube end, respectively, one of three alternative embodiments of a guide arrangement which defines an internal guide channel aligned in tandem with the inlet and outlet ends of the housing along a common axis, and a cylindrical ram movable along the axis for engaging and moving the end plug from the inlet end through the guide channel to the outlet end where the plug is applied to the tube end. The guide arrangement, whether it takes the form of a deformable bushing, a series of radially-mounted inwardly-biased runners or a series of parallel-mounted inwardly-biased rolls, defines the guide channel with a cross-sectional size smaller than that of the end plug and when contacted by the moving plug yieldably expands such that the guide channel conforms to the external surface of the end plug and thereby establishes and maintains guiding contact therewith as the end plug is moved through the guide channel.

This is a divisional of co-pending application Ser. No. 06/678,519 filedon 12-05-84.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the manufacture of nuclearfuel rods to be incorporated into fuel assemblies for nuclear reactorsand, more particularly, is concerned with an improved apparatus forapplying an end plug to a fuel rod tube end such that the end plug isguided in a secured manner into the tube end regardless of where the endplug falls in its diametral tolerance range.

2. Description of the Prior Art

Fuel elements or rods for nuclear reactors commonly encase the fissiblematerial in thin walled cladding or tubes which serve to support thenuclear fuel during the operation of the reactor. The nuclear fuel,which is usually in the form of cylindrical pellets of enriched uraniumdioxide, must be isolated from the environment surrounding the tubes toprevent contact and chemical reactions between the fuel and othermaterials such as water in a pressurized water reactor. Thus, thenuclear fuel is ordinarily hermetically sealed in each thin walled tubeby the use of a pair of opposite end closures or plugs.

It is critical that the end plugs themselves be impermeable andmechanically strong to contain the fissible products. It is equallycritical that the mechanical connection of each end plug with an end ofeach tube be free of defects such as discontinuities, cracks and tubedistortions which could eventually produce leaks.

Present methods of applying the end plugs use close fitting guides toalign the plugs with the tube, such as illustrated in FIG. 2. Due tomanufacturing tolerances, the necessary clearance between the plug andguide sometimes permits the plug to cock, or tip, as shown in solid lineform in FIG. 2, which causes a shaving action on the plug exterior asthe plug is rammed home. Thereafter, when the connection is completedsuch as by welding the plug to the tube, faulty welds commonly resultwhich produce leaking because of discontinuities in the weld joint orconnection caused by this shaving action. Also, frequently the plug doesnot seat properly which increases the likelihood of leakage.Additionally, pieces of the plug are broken off occasionally as it isforced into the tube. The broken pieces not only damage the end plug butalso cause foreign objects to be deposited in the fuel rod.

Consequently, a need exists for an improved technique for applying anend plug to the tubular end of a fuel rod which will accommodate slightvariations in the dimensions of interfitting parts due to unavoidablemanufacturing tolerances and thereby increase the resistance of fuelrods to leakage and failure. SUMMARY OF THE INVENTION

The present invention provides several embodiments of an improvedapparatus for applying an end plug to the end of a fuel rod tube in amanner designed to satisfy the aforementioned needs. In each embodiment,intimate contact is maintained with the end plug by a conformable plugguide means which results in the end plug being securely guided until itenters the hollow tube end. The maintenance of continuous contactbetween the guide means and the end plug prevents the end plug frombeing propelled forward out of contact with a ram member being used tomove the end plug through the guide means and into the tube end. As aresult, the end plug is prevented from cocking, tipping or tumblingwithin the guide means so that it would not meet the tube end squarely.

Accordingly, the present invention sets forth an improved apparatus forapplying an end plug to a hollow tube end of a nuclear fuel rod suchthat a close frictional interfitting engagement will be establishedbetween the end plug and the tube end facilitating the formation of aconnection therebetween which hermetically seals the fuel rod, theimproved apparatus comprising: (a) a housing having spaced inlet andoutlet ends, the inlet end adapted to receive the end plug and theoutlet end adapted to receive the tube end to which the plug is to beapplied; (b) guide means disposed in the housing and having internalsurface portions which define an internal guide channel aligned intandem with the inlet and outlet ends of the housing along a common axisand being of a cross-sectional size smaller than that of an outerexternal surface of the end plug, the guide means being yieldablyexpandable radially with respect to the common axis; and (c) meansdisposed adjacent the inlet end of the housing and movable along thecommon axis for engaging and moving the end plug from the inlet endthrough the guide channel to the outlet end, the movement of the plugthrough the guide channel causing yieldable expansion of thecross-sectional size of the guide means such that the surface portionsof the guide means conform to the external surface of the end plug andmaintain guiding contact therewith as the end plug is moved through theguide channel.

In a first alternative embodiment of the apparatus, the guide means is abushing disposed in the housing which is composed of resilientlydeformable material adapted to expand and conform to the outer externalsurface of the end plug upon contact therewith and thereby establish andmaintain guiding contact with the end plug as it is moved through acentral bore of the bushing which defines the guide channel.

In a second alternative embodiment of the apparatus, a plurality ofelongated runners are mounted for radial movement along a series ofpassageways which are defined in the housing in spaced relationship toone another and extending generally parallel to and radially from thecommon axis. A plurality of resiliently expandable memberscircumscribing the housing and the runners bias them inwardly toward oneanother. However, the members are yieldable to allow movement of therunners away from one another upon contact with the outer externalsurface of the end plug for establishing and maintaining guiding contactwith the end plug as it is moved through the guide channel defined byinner end surfaces of the runners.

In a third alternative embodiment of the apparatus, a plurality ofelongated generally cylindrical rolls are mounted for movement radiallyin a series of recesses which are defined in the housing in spacedrelationship to one another about the common axis and aligned generallyparallel to one another and with the common axis. A plurality ofresiliently expandable elements encircling the housing within respectivecircumferential slots therein which intersect with the elongatedrecesses and stretched about the rolls bias them toward inner ends ofthe recesses. However, the elements are yieldable to allow the rolls tomove away from the inner ends of the recesses upon contact with theouter external surface of the end plug for establishing and maintainingguiding contact with the end plug as it is moved through the guidechannel defined by inner facing surface portions of the rolls.

These and other advantages and attainments of the present invention willbecome apparent to those skilled in the art upon a reading of thefollowing detailed description when taken in conjunction with thedrawings wherein there is shown and described an illustrative embodimentof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the following detailed description, reference will bemade to the attached drawings in which:

FIG. 1 is an elevational view, partly in section, of a fuel assemblyhaving nuclear fuel rods whose end plugs were applied in accordance withthe present invention, the assembly being illustrated in verticallyforeshortened form with parts broken away for clarity.

FIG. 2 is a fragmentary sectional view of a prior art apparatus forapplying an end plug to an end of a fuel rod tube.

FIG. 3 is a fragmentary sectional view taken along line 3--3 of FIG. 4of a first alternative embodiment of the apparatus of the presentinvention for applying an end plug to a fuel rod tube end.

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3.

FIG. 5 is an end view, partly in section, taken along line 5--5 of FIG.6 of a second alternative embodiment of the end plug applying apparatusof the present invention.

FIG. 6 is a sectional view taken along line 6--6 of FIG. 5.

FIG. 7 is an end view, partly in section, taken along line 7--7 of FIG.8 of a third alternative embodiment of the end plug applying apparatusof the present invention.

FIG. 8 is a sectional view taken along line 8--8 of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views. Also in thefollowing description, it is to be understood that such terms as"forward", "rearward", "left", "right", "upwardly", "downwardly", andthe like, are words of convenience and are not to be construed aslimiting terms.

In General

Referring now to the drawings, and particularly to FIG. 1, there isshown an elevational view of a fuel assembly, represented in verticallyforeshortened form and being generally designated by the numeral 10. Thefuel assembly 10 is the type used in a pressurized water reactor (PWR)and basically includes a lower end structure or bottom nozzle 12 forsupporting the assembly on the lower core plate (not shown) in the coreregion of a reactor (not shown), and a number of longitudinallyextending guide tubes or thimbles 14 which project upwardly from thebottom nozzle 12. The assembly 10 further includes a plurality oftransverse grids 16 axially spaced along the guide thimbles 14 and anorganized array of elongated fuel rods 18 transversely spaced andsupported by the grids 16. Also, the assembly 10 has an instrumentationtube 20 located in the center thereof and an upper end structure or topnozzle 22 attached to the upper ends of the guide thimbles 14. With suchan arrangement of parts, the fuel assembly 10 forms an integral unitcapable of being conveniently handled without damaging the assemblyparts.

As mentioned above, the fuel rods 18 in the array thereof in theassembly 10 are held in spaced relationship with one another by thegrids 16 spaced along the fuel assembly length. Each fuel rod 18includes nuclear fuel pellets 24, and the opposite ends of the rod areclosed by upper and lower end plugs 26,28 to hermetically seal the rod.Commonly, a plenum spring 30 is disposed between the upper end plug 26and the pellets 24 to maintain the pellets in a tight, stackedrelationship within the rod 18. The fuel pellets 24 composed of fissiblematerial are responsible for creating the reactive power of the PWR. Aliquid moderator/coolant such as water, or water containing boron, ispumped upwardly through the fuel assemblies of the core in order toextract heat generated therein for the production of useful work.

To control the fission process, a number of control rods 32 arereciprocally movable in the guide thimbles 14 located at predeterminedpositions in the fuel assembly 10. Specifically, the top nozzle 22includes a rod cluster control mechanism 34 having an internallythreaded cylindrical member 36 with a plurality of radially extendingflukes or arms 38. Each arm 38 is interconnected to a control rod 32such that the control mechanism 34 is operable to move the control rods32 vertically in the guide thimbles 14 to thereby control the fissionprocess in the fuel assembly 10, all in a well-known manner.

Hereinafter, the structure and operation of the prior art apparatus andthe improved apparatus for applying the upper and lower end plugs 26,28to the opposite ends of each fuel rod 18 will be described in relationto application of the upper end plug 26 to the upper end 40 of anelongated tube 42 of the fuel rod 18. It should be understood that suchdescription applies equally to the application of the lower end plug 28to a lower end 44 of the fuel rod tube 42.

Prior Art End Plug Applying Apparatus

As mentioned previously, the fuel rods 18 are hermetically sealed toisolate the fissile material contained therein from the surroundingenvironment. In order to ensure a reliable seal, it is important thatthe mechanical connections of the end plugs 26,28 with the opposite ends40,44 of the elongated tube 42 of the fuel rod 18 be free of defectswhich could eventually produce leaks.

With reference to FIG. 2, the mechanical connection of plug 26 to uppertube end 40 is formed by, first, a close frictional interfittingengagement between an external surface 46 of inner cylindrical portion48 of the plug 26 and an internal surface 50 of the upper end 40 of thefuel rod tube 42, and, second, a girth weld (not shown) formed at thelocation of a butt joint of the end edge 52 of the tube upper end 40 andan annular shoulder 54 defined on the end plug 26 by the transitionbetween the inner cylindrical portion 48 and an outer cylindricalportion 56 which has a diameter larger than that of the inner portion48. The outside diameter of the inner insertable portion 48 of the plug26 is slightly greater than the inside diameter of the fuel rod tube 40for producing a friction fit which expands the tube 42 slightly when theend plug inner portion 48 is inserted into the tube end 40. The outsidediameter of the end plug outer portion 56 is such that it is generallyequal to the outside diameter of the end 40 of the tube 42 once thelatter has been expanded by the inserted inner portion 48 of the endplug.

When one prior art end plug applying apparatus is used, such as shown inFIG. 2 and generally designated by the numeral 58, occasional damagewould occur at edge portions of the end plug 26 and/or end 40 of thefuel rod tube 42. As seen in FIG. 2, the prior art apparatus 58 includesan elongated hollow cylindrical guide bushing 60 having inserted intoits open end 62 the upper end 40 of the fuel rod tube 42 to which theend plug 26 is to be applied. A cylindrical ram 64, only fragmentarilyshown in FIG. 2, is reciprocally moved within the bushing 60 by aconventional source of power (not shown), such as hydraulic or pneumaticpressure, between a retracted position and an extended position.

In the retracted position of the ram 64, as seen in solid line form inFIG. 2, its leading face 66 is located to the left of an upper entranceopening 68 defined in the bushing 60. The opening 68 communicates theinterior of the bushing 60 with a magazine (not shown) containing avertical stack of end plugs 56 (the lower one of which is shown infragmentary dashed outline form at 26a in FIG. 2). When the ram 64 is inits retracted position, the end plug fed from the magazine enters theopening 68 and is deposited at a loading position (as seen in dottedoutline form at 26b in FIG. 2) in front of the leading face 66 of theram.

The ram 64 is then actuated to move forwardly past the opening 68 andtoward the open end 62 of the bushing 60 to its extended position (notshown) in which the end plug is applied to the upper end 40 of the fuelrod tube 42 (as seen in dotted outline form at 26c in FIG. 2). The tube42 is securely clamped by suitable means (not shown) at the open end 62of the bushing 60 to withstand axial insertion forces which can exceed500 pounds. During the forward stroke of the ram 64 (such as exemplifiedby the position of its leading face, as shown in dashed outline form at66a in FIG. 2, intermediately of the retracted and extended positions ofthe ram) in which the end plug is carried ahead of it, occasionally theplug cocks, tips or tumbles (as seen in solid line form at 26 in FIG. 2)so that it does not meet the upper end 40 of the fuel rod tube 42squarely. This can occur if the plug 26 is at the low end of itstolerance range and the guide bushing 60 is at the high end of itstolerance range. It can also occur if the motion of ram 64 is uneven. Inthe latter instance, the plug 26 will be propelled forward, losingcontact with the leading face 66 of the ram 64. (Continuous contact withthe ram face 66 tends to keep the plug 26 aligned with the tube end 40).

Cocking or tipping of the upper end plug 26 (as compared to the lowerend plug 28) is worsened by the presence of the plenum spring 30 at theupper end of the tube 42 which tends to resist application of the upperplug 26 to the upper tube end 40. As a consequence, the plug 26 does notseat properly, and oftentimes pieces of the plug 26 or upper tube end 40are broken off as the inner cylindrical end portion 48 of the plug 26 isforced into the tube 42 (as seen at 26c in FIG. 2). The broken piecesnot only damage the end plug 26, but also cause foreign objects to bedeposited in the fuel rod 18. While normally the plenum spring 30 isonly in the upper end 40 of the fuel rod tube 42, the same problems ofcocking and tipping occur where there is no spring present at the lowerend 44 of the tube 42.

Improved End Plug Applying Apparatus

The apparatus of the present invention, three alternative embodiments ofwhich are disclosed herein, eliminates the problems associated with theabove-described prior art apparatus 58 which were caused primarily bythe annular clearance between the external surface 70 of the outerportion 56 of the end plug 26 and the internal surface 72 of the guidebushing 60. In each of the alternative embodiments of the improved endplug applying apparatus of the present invention, which will now bedescribed in detail, a guide means is provided having internal surfaceportions which define an internal guide channel which has a diameterless than the smallest allowable (or tolerable) plug diameter for theouter portion 56 of the end plug 26. Thus the external surface 70 of theplug 26 will always be in guiding contact with the guide channel of theguide means. The guide means is thereby conformable so that it providesintimate contact with the end plug 26 regardless of where the plug fallsin its diametral range of tolerance.

Turning now to FIGS. 3 and 4, there is shown the first alternativeembodiment of the improved end plug applying apparatus of the presentinvention, being generally indicated by the numeral 74. The end plugapplying apparatus 74 basically includes a housing 76, guide means inthe form of a resiliently deformable bushing 78, and plug moving meanssuch as a cylindrical ram 80.

The housing 76 is in the form of a cylindrical cup 82 having anoutwardly-turned annular flange 84 encompassing its mouth end 86 and anopening 88 formed in its opposite bottom end 90. The housing 76 alsoincludes a cylinder 92 within which the ram 80 is reciprocally moved byany suitable source of power, such as hydraulic or pneumatic pressure asmentioned above. Specifically, the cylinder 92 has an end flange 94against which the mouth end 86 of the housing cup 82 is placed and towhich the cup is attached by a series of bolts 96 used to securelyfasten the cup flange 84 to the periphery of the cylinder flange 94.

The housing 76 has spaced inlet and outlet ends 98,100 adapted toreceive the end plug 26 and tube end 40, respectively. The inlet end 98of the housing 76 is defined by the open end of the cylinder 92surrounded by the end flange 94. The cylinder 92 also has an upperopening 102 immediately behind the end flange 94 through which the endplug (as seen in dashed outline form at 26d in FIG. 3) is deposited by afeed magazine (not shown) into a loading position in front of theleading face 104 of the ram 80. The outlet end 100 of the housing 76 isdefined by the opening 88 formed in the bottom end 90 of the housing cup82.

The resiliently-deformable bushing 78 forming the guide means of thefirst alternative embodiment of the improved apparatus 74 is disposed inthe housing 76 and aligned in tandem with the inlet and outlet ends98,100 of the housing along a common axis 106. The bushing 78 has acontinuous internal side wall 108 defining a central bore 110 in coaxialalignment with the housing inlet and outlet ends 98,100. The internalside wall 108 defines the guide channel of the guide means and has across-sectional size, i.e. diameter, smaller than that of the outerexternal surface 70 of the outer portion 56 of the end plug 26.

The bushing 78, due to being composed of resiliently deformablematerial, such as urethane, is adapted to expand and conform to theouter external surface 70 of the end plug 26 upon contact therewith.Thus, when the ram 80 is moved along the common axis 106, its leadingface 104 engages and moves the end plug 26 from the inlet end 98 of thehousing 76 through the guide channel defined by central bore 110 to theoutlet end 100 of the housing. The movement of the end plug 26 throughthe central bore 110 causes yieldable expansion of the cross-sectionalsize of the bore such that the internal side wall 108 (which includesthe surface portions defining the guide channel) conforms to theexternal surface 70 of the end plug 26 and thereby establishes andmaintains guiding contact therewith as the end plug is moved through thebore 110 of the bushing 78.

In one exemplary form of the first alternative embodiment of theimproved apparatus 74, the housing cup 82 is bored out to form a portionof a mold for casting the guide bushing 78 in place. The housing 76 plustwo core pieces (not shown) comprise the mold. The mold core pieces aresized about 0.001" below the minimum plug major diameter. The amount ofinterference thus varies from 0.001" to 0.003". The mold core pieces areground and polished. This results in an exceptionally smooth bore 110 inthe cast urethane bushing 78. The long wearing characteristic of theurethane material should result in a long service life for the bushing78. Also, the bushing 78 is cast with a tapered entrance and exitsections 112,114. A step can be added to act as a guide for tube end 40if desired.

Referring now to FIGS. 5 and 6, there is shown the second alternativeembodiment of the improved end plug applying apparatus of the presentinvention, being generally indicated by the numeral 116. The end plugapplying apparatus 116 basically includes a housing 118, guide means inthe form of a plurality of runners 120 and resiliently expandablemembers 122, and end plug moving means such as a cyclindrical ram 124.

The housing 118 is in the form of a cylindrical fixture 126 havingrespectively defined therein a series of peripheral recesses 128, aseries of elongated passageways 130, and a central hole 132. The housing118 also includes a base 134 having a central opening 136 and to whichis integrally connected the feed chute 138 of a magazine for supplyingend plugs 26 to the central opening 136 in the housing base. The fixture128 and base 134 of the housing 118 are attached together by a series ofbolts 140 located within the recesses 128 which securely fasten thefixture 128 to spaced locations on the base 134 so as to align theirrespective central hole 132 and opening 136 along a common axis 142.

The housing 118 has spaced inlet and outlet ends adapted to receive theend plug 26 and the tube end 40, respectively. The inlet end of thehousing 118 is defined by the central opening 136 of the base 134, whilethe outlet end is defined by a central tapered hole 144 of circularplate 146 attached to the fixture 126 by a series of bolts 148 on a sideopposite from the base 134. The radial passageways 130 within thefixture 126 are defined between the plate 146 and a circular wallportion 149 of the fixture which lies flush against the base 134.Furthermore, the passageways 130 are spaced from one another about thecommon axis 142 and extend generally parallel to and radially from theaxis 142.

Each of the plurality of runners 120 of the improved apparatus 116 ismounted in one of the passageways 130 in the housing 118 such that therunners 120 are maintained spaced apart from one another about the axis142, extend generally parallel to and radially from the axis 142, andare move radially toward and away from the axis. The runners 120 haveouter portions 150 extending outwardly from the passageways 130 andinner portions 152 extending inwardly from the passageways. The innerrunner portions define longitudinally-extending inner surfaces 154exposed to and facing one another so as to define the guide channel forthe end plug 26 therebetween. In an exemplary form, the runners 120 canbe fabricated from hardened, chrome-plated and polished material withtapered lead-ins on opposite edges of their inner portions 152. Also,the edge 155 on each runner 120 adjacent the base 134 is caged by thecircular wall portion 149 of the fixture 126 so as to limit radialmovement of the runner 120 within the passageway 130 away from the axis142.

Circumscribing the housing 118, and stretched about the outer runnerportions 150 in arcuate depressions 156 therein is the plurality ofresilient expandable members 122, which can take any suitable form, suchas garter springs or elastomer bands, for instance. The members 122 biasthe runners 120 inwardly toward one another so as to maintain thecross-sectional size of the guide channel formed between the innersurfaces 154 on runner inner portions 152 less than the cross-sectionalsize of the outer portion 56 of the end plug 26. The material of themembers 122 is stretchable and, thus, when the ram 124 is moved alongthe common axis 142 and its leading face 158 engages and moves the endplug from its initial position (as seen in dashed outline form at 26e inFIG. 6) into the guide channel, the members 122 yieldably allow movementof the runners 120 away from one another upon contact of the innersurfaces 154 thereof with the outer external surface 70 of the end plug26. In such manner, the runner inner surfaces 154 defining the guidechannel conform to the external surface 70 of the end plug 26 andthereby establish and maintain guiding contact therewith as the end plugis moved from the inlet to the outlet ends of the housing 118 to wherethe end plug is applied to the tube end 40.

Turning finally to FIGS. 7 and 8, there is shown the third alternativeembodiment of the improved end plug applying apparatus of the presentinvention, being generally indicated by the numeral 160. The end plugapplying apparatus 160 basically includes a housing 162, guide means inthe form of a plurality of rolls 164 and resiliently expandable elements166, and plug moving means such as a cylindrical ram 168.

The housing 162 is in the form of a cup-shaped cap 170, a base 172, anda hub assembly 174 disposed within the cap 170 and having an end flange176 interposed between the cap 170 and base 172 with a series of bolts178 securely fastening the cap 170, base 172 and hub flange 176together. The base 172 has a central opening 180 which is aligned with acenter bore 182 in a hub 183 of the hub assembly 174 along a common axis184. A feed chute 186 of a magazine for supplying end plugs 26 to thecentral opening 180 in the base 172 is integrally connected thereto.

The housing 162 has spaced inlet and outlet ends adapted to receive theend plug 26 and the tube end 40, respectively. The inlet end of thehousing 162 is defined by the central opening 180 of the base 172, whilethe outlet end is defined by a central hole 188 in the outer end 190 ofthe cap 170. The hub 183 is aligned with and extends into the centralhole 188 of the cap 170. A series of elongated recesses 192 are definedin the hub 183, spaced from one another about the common axis 184 andaligned generally parallel to one another and with the axis 184.

Furthermore, the hub 183 is spaced radially inwardly from a continuouscylindrical wall 194 of the cap 170 which provides an annular space 196therebetween. The hub assembly 174 includes a series of annular rings198 disposed about and spaced along the hub 183 and fixed thereto by setscrews 200 so as to define a series of circumferential slots 202 spacedfrom one another along the common axis 184 and intersecting theelongated recesses 192.

Each of the plurality of elongated generally cylindrical rolls 164 ofthe improved apparatus 160 is mounted in one of the recesses 192 in thehub 183 such that the rolls are maintained spaced apart from one anotherabout the common axis 184, disposed generally parallel thereto and toone another, and are movable radially toward and away from the axis.Each recess 192 has an inner end 204 defining an elongated opening 206of a width less than that of the roll 164 such that the rolls havelongitudinally-extending surface portions 208 exposed to and facingtoward one another through the openings 206 so as to define the guidechannel for the end plug 26 therebetween. In an exemplary form, therolls 164 can be fabricated from hardened, chrome-plated and polishedmaterial with tapered lead-ins on opposite ends thereof. Also, the rolls164 are caged by the portions of the annular rings 198 which overlie therecesses 192 so as to limit radial movement of the rolls within therecesses away from the axis 184.

Circumscribing the housing 162 within the respective circumferentialslots 202 formed by the annular rings 198, and stretch about the rolls164, is the plurality of resilient expandable elements 166, which cantake any suitable form, such as garter springs or elastomer bands, forexample. The elements 166 bias the rolls 164 inwardly toward one anotherand toward the inner ends 204 of the recesses 192 so as to maintain thecross-sectional size of the guide channel formed between the innersurface portions 208 of the rolls less than the cross-sectional size ofthe outer portion 56 of the end plug 26. Due to the material of theelements 166 and, thus, when the ram 168 is moved along the common axis184 and its leading face 210 engages and moves the end plug from itsinitial position (as seen in dashed outline form at 26f in FIG. 8) intothe guide channel, the elements 166 yieldably allow deflection ormovement of the rolls 164 away from one another upon contact of theinner surface portions 208 with the outer external surface 70 of the endplug 26. In such manner, the roll inner surface portions 208 definingthe guide channel conform to the external surface 70 of the end plug 26and thereby establish and maintain guiding contact therewith as the endplug is moved from the inlet to the outlet ends of the housing 162 towhere the end plug is applied to the tube end 40.

It is thought that the present invention and many of its attendantadvantages will be understood from the foregoing description and it willbe apparent that various changes may be made in the form, constructionand arrangement thereof without departing from the spirit and scope ofthe invention or sacrificing all of its material advantages, the formshereinbefore described being merely a preferred or exemplary embodimentsthereof.

We claim:
 1. An end plug applying apparatus for applying an end plug toa hollow tube end of a nuclear fuel rod such that a frictionalinterfitting engagement will be established between the end plug and thetube end facilitating the formation of a connection therebetween whichhermetically seals the fuel rod, said apparatus comprising:(a) a housinghaving spaced inlet and outlet ends, said inlet end adapted to receivethe end plug and said outlet end adapted to receive the tube end towhich the plug is to be applied; (b) guide means disposed in saidhousing and having internal surface portions which define an internalguide channel aligned in tandem with said inlet and outlet ends of saidhousing along a common axis and being of a cross-sectional size smallerthan that of an outer external surface of the end plug, said guide meansbeing yieldably expandable radially with respect to said common axis;(c) means defining an infeed opening adjacent said inlet end of saidhousing and displaced laterally of said common axis through which theend plug is fed in a direction extending toward said common axis to aloading position in front of said inlet end of said housing; and (d)means disposed adjacent said inlet end of said housing and movable alongsaid common axis for engaging and moving the end plug from said loadingposition in front of said inlet end, through said inlet end and throughsaid guide channel, to said outlet end, said movement of said plugthrough said guide channel causing yieldable expansion of thecross-sectional size of said guide means such that said surface portionsof said guide means conform to the outer external surface of the endplug and maintain guiding contact therewith as the end plug is movedthrough said guide channel; (e) said housing includesa series ofelongated recesses spaced from one another about said common axis andaligned generally parallel to one another and with said common axis, anda series of circumferential slots spaced from one another along saidcommon axis and intersecting said elongated recesses; and said guidemeans includinga plurality of elongated generally cylindrical rolls,each roll being mounted in one of said recesses such that said rolls aremaintained spaced apart from one another about said common axis,disposed generally parallel thereto and to one another and movableradially toward and away from said common axis, said each recess havingan inner end defining an elongated opening of a width less than that ofsaid roll such that said rolls have longitudinally-extending surfaceportions exposed and facing toward one another through said openings soas to define said guide channel therebetween, and a plurality ofresiliently expandable elements circumscribing said housing within saidrespective circumferential slots therein and stretched about saidplurality of rolls so as to bias said rolls toward said inner ends ofsaid recesses, said elements yieldably allowing movement of said rollsaway from said inner ends of said recesses upon contact of said facingsurface portions of said rolls with the outer external surface of theend plug for establishing and maintaining guiding contact with the endplug as the same is moved through said guide channel between said inletand outlet ends.
 2. End plug applying apparatus as recited in claim 1,wherein said expandable elements take the form of a series of endlessbands.
 3. End plug applying apparatus as recited in claim 1, whereinsaid housing includes a hub assembly comprising:a central hub havingsaid series of recesses defined therein; and a series of annular ringsdisposed about and spaced along said hub so as to define said series ofcircumferential slots which intersect said recesses.